Can I prevent TStringlist removing key value pair when value set to empty

Question

Can I prevent TStringList from removing key-value-pair when value is set to empty? I use Delphi XE8 and Lazarus which work differently. I want the pair to be left in the TStringlist object even when the value is set to an empty string. For example:

procedure TMyClass.Set(const Key, Value: String);
begin
  // FData is a TStringList object
  FData.Values[Key] := Value; // Removes pair when value is empty. Count decreases and Key is lost.
end;

Problem that I'm having is that when I compile with Delphi the pair with empty values is removed and I don't know afterwards was a value with a key never set or was it explicitly set to be an empty string. Also I can't get all the keys that have been used. Now I need to hold another collection of keys that holds information about empty ones.

MyKeyValues.Set('foo', 'bar'); // Delphi FData.Count = 1; Lazarus FData.Count = 1
MyKeyValues.Set('foo', '');    // Delphi FData.Count = 0; Lazarus FData.Count = 1

Answer 1

You can write a class helper to implement a new behaviour of the SetValue method of the TStrings class.

If you don't like a solution based on a class helper, you can use a custom class which inherits from TStringList and, again, override its Values property behaviour - the code is very similar to this helper-based implementation.

I'd prefer to use the second choice because the helper will define a new behaviour for all the TStringList objects.

type
  TStringsHelper = class helper for TStrings
    private
      function GetValue(const Name: string): string;
      procedure SetValue(const Name, Value: string); reintroduce;
    public
      property Values[const Name: string]: string read GetValue write SetValue;
  end;


function TStringsHelper.GetValue(const Name: string): string;
begin
  Result := Self.GetValue(Name);
end;

procedure TStringsHelper.SetValue(const Name, Value: string);
var
  I: Integer;
begin
  I := IndexOfName(Name);
  if I < 0 then I := Add('');
  Put(I, Name + NameValueSeparator + Value);
end;

Answer 2

What about this?

procedure TMyClass.Set(const Key, Value: String);
var
  i:integer;
begin
  i := FData.IndexOfName(Key);
  if i = -1 then
    FData.Add(Key + '=' + Value)
  else
    FData[i] := Key + '=' + Value;
end;

You can choose wether to set FData.Sorted:=true; or not.